Communications in a safety system require very high reliability and very low latency. Therefore, the communications are conventionally performed using dedicated wired medium. For example, in an elevator system, in order to send safety messages between a controller and an elevator car, a heavy communication cable is suspended in the shaft, and moves along with the car. As building height increases, the weight and cost of the communication cable increases significantly. As the weight increases, power consumption for the elevator system also increases. Building height has a multiplicative effect on total cost and power consumption of elevator systems. A lower cost and more energy efficient solution is desired for safety systems in elevator systems. A possible solution is to replace wired communications by wireless communications.
To ensure the safety of elevator passengers, the International Electronic Commission (IEC) has published stringent safety and reliability requirements for elevator communication networks that only allow one error in a quadrillion (1015) safety related messages. However, wireless communication is subject to external interference and variable wireless channel conditions. In addition, wireless communication has a limited transmission range, especially in indoor settings. Therefore, it is very challenging to apply wireless communications to safety systems for elevator systems.
Therefore, it is desired to provide a reliable wireless communication network that satisfies stringent safety and reliability requirements for elevators, and other similar safety systems.